Subshell Differential Photoionization Studies of Single- and Multi-Walled Fullerene Endohedrals

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The encapsulation of atoms in fullerenes offers a unique natural laboratory to examine the behavior of an atom in confinement. Studies of these endohedral compounds can not only lead to intriguing effects at the atomic scale but also can probe subtleties of quantum effects in the nanometer region. Besides the single-wall confinement, the multi-walled confining shell of nested concentric single-walled fullerenes, bucky-onions,can make the coupling of the central atom with the shell rich in novel effects.Technologically also the endohedral fullerenes hold the promise of exciting applications:(a) Research is underway to use endohedrally doped fullerenes and bucky onions as seed materials in solid state quantum computations, in which quantum bits can be encoded in the electronic and nuclear spins of the encapsulated atoms. (b) Recent experiments with Ar@C60 find evidence of encaged atoms significantly improving the superconducting ability of materials. (c) A proposed biomedical application of endohedral materials is to shield radioactive tracers inside fullerene cages, and then inject the material into human blood to monitor blood flow. (d) The ability of fullerenes to sequester metal atoms inside has led to exploring their potential as contrast-enhancing agents for magnetic resonance imaging. The discovery of endo fullerenes with trapped noble gases in extraterrestrial environments indicates the astrophysical relevance of their studies. Therefore, understanding the influence of the confining cage on thespectroscopy of the atom inside, and vice versa, are matters of significant interest.A theoretical photoionization study of these compounds is proposed. Photoionization is a well known method to obtain a fairly undistorted account of the many-electron dynamics of the discrete and continuum states of atomic systems, since the coupling of the photon with the electrons is so weak and the photon disappears in the final channel.Employing this tool we will investigate the role of the collective motion of delocalized electrons in endohedrally doped single- and multi-walled fullerenes. Cross sections and asymmetry parameters of the ionization from both atomic and fullerene sub-shells will be calculated to understand the many-body interactions that determine the photoabsorption properties of these nanoparticles.Moreover, the diffraction of atomic photo-liberated electrons in crossing the confining wall will be studied in detail in the spirit of a recently discussed Fourier photo-spectroscopy approach.